Your piano is made primarily of wood, a versatile and beautiful material ideal for piano construction. However, being made of wood, your piano is greatly affected by humidity. Seasonal and even daily changes in humidity cause wood parts to swell and shrink, affecting tuning stability and touch. Extreme swings in humidity can eventually cause wood to crack and glue joints to fail.

Other materials in your piano also are affected by changes in moisture content in the air. The many felt and leather parts in your piano's action can change dimension, affecting regulation and friction, or stiffness of the touch. Very high humidity can even create condensation on metal parts such as strings, tuning pins and hardware, eventually causing them to rust.

How does humidity level affect my piano's tuning?

Swelling and shrinking of the piano's soundboard is the most immediate and noticeable effect of humidity change. The soundboard, a sheet of wood approximately 3/8 of an inch thick, is made with a slightly crowned shape. The strings pass over the soundboard and are connected to it by a wooden piece called a bridge. The upward crown of the soundboard presses the bridge tightly against the strings.

As the moisture level in the soundboard increases during periods of high relative humidity, the crown expands and pushes the bridge harder against the strings. The strings are stretched tighter and the piano's pitch rises. Because this increase in crown is greater in the center of the soundboard than at the edges, the pitch rises more in the middle octaves than in the bass or treble registers.

During periods of low relative humidity the soundboard shrinks, reducing the crown and decreasing pressure against the strings. The pitch drops, again with the greatest effect noticeable in the center of the keyboard. When relative humidity returns to its previous level, the average pitch of all the strings will return to normal, although the exact pitch of individual strings will be slightly changed from their original settings. Thus, a piano only will stay in tune as long as the relative humidity level in the air surrounding the soundboard remains constant. Extreme humidity changes require making greater changes in string tension to bring the piano into tune. This upsets the equilibrium between the string tension and the piano frame, and the piano never becomes stable.

What is relative humidity?

Wood swells and shrinks in response to changes in the relative humidity of the air around it. Relative humidity (RH) is the amount of moisture contained in the air, compared to the maximum amount of moisture that the air is capable of holding. The moisture content of air is affected by weather as well as conditions and activities within the home, while the moisture- holding capacity of air varies with temperature. One way of thinking about RH is that it is a measure of air's tendency to absorb or release moisture to its surroundings. Thus when the RH of air in a room increases, moisture will tend to transfer from the air to wood and other absorbent materials in the room. When the RH of air decreases, moisture will transfer from other materials back into the air. The RH of the atmosphere is always changing by the hour, and more dramatically, with the seasons. Consequently, the wood and felt parts in your piano are constantly changing dimension as they absorb and release moisture.

Since RH depends upon the temperature and moisture content of the air, it is not possible to maintain a constant RH by controlling room temperature alone. In fact, maintaining an even temperature while moisture content varies will cause RH to change.

What can be done to minimize humidity problems?

Keeping the humidity level around your piano as constant as possible will help it stay in tune longer as well as slow such damage as soundboard cracks, loose tuning pins, and glue joint failures. The first and simplest precaution you can take is to position your piano away from areas where it would be exposed to extremes of temperature and humidity such as heating and cooling vents, stoves, doors and windows. Direct sunlight is especially damaging. If your home is not well insulated, an interior wall is preferable to an outside wall.

Controlling the humidity within the home is another step you can take to preserve your instrument. In most areas of the country the relative humidity is very low during the cold winter season, and very high during the spring and summer. In other areas these humidity cycles are reversed. Wherever you live, you have probably noticed the symptoms of low RH (shocks from static electricity when sliding out of a car or after walking across carpet), and the signs of high RH (limp, soggy feeling newspapers and sticking doors). To monitor RH changes in your home, you may wish to purchase a moderately priced wall hygrometer available from most instrument supply companies or electronics stores.

Use of a room humidifier during dry seasons will help somewhat. However, too much moisture added to a room during winter months can cause condensation to form on cold surfaces such as windows, eventually causing mildew, rot, and in extreme cases, damage to the building structure. During the humid season de- humidification is needed. If your humid season is winter, keeping the home evenly heated will help. However, humid summer situations require much more elaborate de- humidification systems. Unfortunately, it is seldom possible to adequately control the relative humidity of a piano by controlling the room environment alone.

A very practical and effective answer to humidity problems is to have a humidity control system installed in the piano itself. These systems consist of three parts: a humidifier for adding moisture to the air, a dehumidifier for eliminating excess moisture, and a humidistat or control unit which senses the RH of the air within the piano and activates the system to add or remove moisture as needed. These systems are designed to maintain the RH of the air within the piano at the ideal level of 42%. The components are installed out of sight, inside the case of a vertical piano or under the soundboard of a grand. They are easy to maintain, and can be installed by your piano technician.

How will humidity control benefit my piano?

While not eliminating the need for regular piano maintenance, humidity control will allow more stable tunings by reducing the radical pitch changes your piano may experience through the seasons. When your piano stays closer to its correct pitch level of A440 (A-440 cycles per second), your technician does not have to perform a large pitch raising or lowering procedure prior to fine tuning. Thus, a balance of forces is maintained between the strings and the frame of the piano, allowing more accurate and stable tunings to be done.

In addition, a stable environment will help to preserve your piano through the years. Wood parts, glue joints, metal parts and your piano's finish will all last longer if not subjected to excessive humidity swings. Maintaining the correct environment will preserve your piano investment for a lifetime of enjoyment.

Humidity and the Climate

Excessive humidity and extreme temperature changes are the enemies of the piano. The piano is basically a wooden instrument. Too much moisture in the air will cause the keys and action parts to swell, resulting in sticking and sluggish notes. The felts will, over time, become hard, resulting in a noisy action. The tuning pin block–a laminated hardwood block into which the tuning pins are driven, will expand around those pins, and then, when the surrounding are becomes dry and the block loses some of its moisture, will contract, causing the tuning pins to become loose, resulting in a piano that will not "hold a tune." The steel strings will become rusty and destroy the tone of the instrument. The other metal parts will, likewise, rust and eventually need to be replaced.

The ideal level of humidity for a piano is around 40 per cent. While it is almost impossible to maintain a particular level of humidity in a home, certain precautions can be taken. Don’t place the piano near a window or door where it will be exposed to dramatic changes in outside humidity. Don’t place the piano near an air-conditioning/heating duct. Don’t place the piano near a fireplace or other source of heat, which will dry out the air.

This brings us to the second "enemy"–extreme temperature change. Many of the things mentioned above relate to temperature change as well as humidity. While humidity changes will alter the tuning of the piano, temperature changes will "knock" a piano out of tune even faster. Do not locate a piano where it will be exposed to direct sunlight. Not only will the sunlight fade the finish, but the piano will go "out of tune" in an incredibly short time. Placing a piano on an outside wall was, in years past, a "no-no." Insulation techniques and air circulation were poor, and methods of heating were such that a piano would "sweat" when placed against an outside wall. However, with today’s central air conditioning, this is not nearly so much a problem.

Protecting Against Humidity

One excellent way to deal with the humidity problem is to have your technician install a piano de-humidifier. This device consists of a long aluminum tube containing a heating element which heats to about the temperature of a hot-water pipe, and a humidistat, which turns the heating element on when the humidity level gets above 40% and off when the level falls below 40%. The entire unit is installed inside the lower cabinet of a vertical piano, or suspended directly underneath a grand piano. Power consumption is negligible, and the unit will last for many years. A humidifier is also available, which plugs into the same humidistat. The humidifier is, in most cases, not really necessary in the Houston climate.

Q. Would New Mexico's climate serve as a good example of an extreme climate that would affect my piano?

A. An excellent example. This climate is a good example that provides wide (often wild) swings in temperature and humidity. Pianos like consistent temperature and humidity levels. What to do?

1) Temperature:

a) Locate your piano against an inside wall.b) Keep your piano out of direct sunlight.c) Keep your piano away from drafts, heat sources and air conditioning vents.d) Keep your piano as far as possible from any fireplace or wood-burning stove. Fire sucks moisture out of the air-and your piano-faster than you can say, "My soundboard cracked!"

2) Humidity: (with a little humour added)

a) Keep your piano in a sealed room with a special humidifier that keeps the room humidity at 42% (manufacturers' recommendation) while making no noise, or . . .b) install an indoor swimming pool, or . . .c) install a Piano Lifesaver Climate Control System from DAMPP-CHASER. I consider these systems so essential to piano care in New Mexico and similar areas. Or . . .d) do nothing-and pray.

To summarize:Ideally, a piano should be kept in a room with temperature around 70°( ± 5°) and relative humidity around 50% (±5%). The exact temperature and humidity is not as important as keeping as little fluctuation as possible. Some pianos react to conditions differently. Yamaha and Kawai are known to have moisture proof treated felt parts in an attempt to avoid some problems with changes due to humidity excursions. The DAMPP-CHASER Humidistat system is probably the best general system for establishing consistent humidity levels in extreme environments. KeyArts / Japan Pianos U.S.A. furnishes this system for our customers or consult your local piano technician.